Title says it, won't work at all in extension and won't recognise anything in desktop app!
PS have uninstalled reinstalled using absolute latest plugin as per other threads tried in various interations. Also the link from desktop app to install the firefox plugin is non functional. For a premium subscription product this is absolutley ridiculous, definitely considering other options...
I can only tell you that I am aware of this issue and if you look at simialr past threads our Dev team is already working on a fix for this. A fix should be released within one of our upcoming new versions.
Can you send me a short video of how this is crashing and not letting you install True Key from the Firefox browser?